A typical LCD has the advantages of portability, low power consumption, and low radiation. LCDs have been widely used in various portable information products, such as notebooks, personal digital assistants (PDAs), video cameras and the like. Furthermore, the LCD is considered by many to have the potential to completely replace CRT (cathode ray tube) monitors and televisions.
Referring to FIG. 4, a typical LCD 10 includes an LCD panel (not labeled), a gate driving circuit 11, and a data driving circuit 12. The LCD panel includes a first substrate (not shown), a second substrate (not shown), and a liquid crystal layer (not shown) sandwiched between the two substrates.
The first substrate includes a number of gate lines 13 that are parallel to each other and that each extend along a first direction, and a number of data lines 14 that are parallel to each other and that each extend along a second direction orthogonal to the first direction. The smallest rectangular area formed by any two adjacent gate lines 13 together with any two adjacent data lines 14 defines a pixel unit 16 thereat. The gate driving circuit 11 is configured for providing a number of scanning signals to the gate lines 13. The data driving circuit 14 is configured for providing a number of gradation voltages to the data lines 14.
In each pixel unit 16, a TFT 15 is provided in the vicinity of a respective point of intersection of one of the gate lines 13 and one of the data lines 14. The TFT 15 functions as a switching element. A pixel electrode 151 is connected to the TFT 15. The second substrate includes a number of common electrodes 152, each common electrode corresponding to a respective one of the pixel electrodes 151 on the first substrate.
When the LCD 10 works, gradation voltages are applied to the pixel electrodes 15 and a common voltage is applied to the common electrodes 152. Thus an electric field is generated and applied to liquid crystal molecules of the liquid crystal layer. At least some of the liquid crystal molecules change their orientations, whereby the liquid crystal layer provides anisotropic transmittance of light therethrough. Thus the amount of the light penetrating the second substrate is adjusted by controlling the strength of the electric field. In this way, desired pixel colors are obtained at the second substrate, and the arrayed combination of the pixel colors provides an image viewed on LCD panel of the LCD 10.
If the electric field between the pixel electrodes 151 and the common electrodes 152 continues to be applied to the liquid crystal material in one direction, the liquid crystal material may deteriorate. Therefore, in order to avoid this problem, gradation voltages that are provided to the pixel electrodes 151 are switched from a positive value to a negative value with respect to the common voltage. This technique is referred to as an inversion drive method.
The inversion drive method needs the common voltage to be a predetermined constant value in order to prevent a flicker phenomenon from appearing on the screen of the LCD 10. Thus a common voltage adjusting method is needed.
However, a typical common voltage adjusting method needs a human operator to alter the common voltage according to a degree of the flicker phenomenon. In other words, the operator needs to personally detect the flicker phenomenon of the LCD 10, and then adjust the common voltage according to the degree of the flicker phenomenon present as judged by the operator himself/herself. Thus, the adjusting procedure for suppressing the flicker phenomenon is subject to human error.
It is desired to provide a common voltage adjusting method for an LCD which can overcome the above-described deficiencies.